Failure of voluntary activation of the quadriceps femoris muscle after patellar contusion.

STUDY DESIGN: Descriptive study of phenomenon.

OBJECTIVES: To determine the extent of failure of voluntary activation of the quadriceps femoris muscle in patients early after patellar contusion.

BACKGROUND: Pain and effusion are related to the presence of quadriceps inhibition. We hypothesized that patients with patellar contusions would be unable to fully recruit their quadriceps muscles and that the activation deficit would be associated with self-report measures of function.

METHODS AND MEASURES: Sixteen patients who had sustained a unilateral patellar contusion fewer than 4 months prior to testing participated in the study (7 men, 9 women; mean age = 30.0 +/- 11.6). Subjects completed a self-report questionnaire to assess knee function and performed an isometric burst superimposition test on the involved and uninvolved quadriceps at 60 degrees of knee flexion. The subjects were assigned to 2 groups according to the presence (n = 5) or absence (n = 11) of quadriceps inhibition.

RESULTS: Sixty-nine percent of the subjects tested were able to fully activate their quadriceps. Both groups had a decreased knee extensor force on the involved side compared to the uninvolved, but the group with inhibition had a lower side-to-side percentage of knee extensor force (mean = 65.5% +/- 18.9) than those without inhibition (mean = 85.5% +/- 16.4).

CONCLUSION: Early after patellar contusion, approximately one-third of the patients demonstrated quadriceps inhibition. According to our working hypothesis, the majority of the patients tested should have demonstrated inhibition. Quadriceps inhibition was not associated with the activities of daily living, sports activity, or global rating scales in this study. Decreased volitional quadriceps force production (the hallmark of inhibition) was the only variable that discriminated patients with patellar contusion who had inhibition from those who did not.